Method for controlling an exhaust-gas aftertreatment device of a hybrid drive, and hybrid drive

ABSTRACT

A method for controlling an exhaust gas aftertreatment device of a vehicle hybrid drive is provided. The method comprises operating the hybrid drive only by a combustion engine, only by a non-combustion motor, or by both, as a function of a temperature of the exhaust aftertreatment device, and conducting exhaust gas of the hybrid drive at least partially through the exhaust aftertreatment device, the engine and motor each providing output to power the vehicle. In this way, the aftertreatment device may be operated at an optimal temperature for conversion performance.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/247,849, “METHOD FOR CONTROLLING AN EXHAUST-GAS AFTERTREATMENTDEVICE OF A HYBRID DRIVE, AND HYBRID DRIVE,” filed Sep. 28, 2011, whichclaims priority to German Patent Application No. 102010037924.7, filedOct. 1, 2010, the entire contents of each of which are herebyincorporated by reference for all purposes.

FIELD

The present disclosure relates to a method for controlling anexhaust-gas aftertreatment device of a hybrid drive.

BACKGROUND AND SUMMARY

It is generally known, in order to reduce the pollutant emissions, totreat the exhaust gases of a combustion engine, for example of an Ottoor diesel engine, by an exhaust-gas treatment device arranged in theexhaust tract. Here, the efficiency of the exhaust-gas aftertreatmentdevice is influenced very decisively by the temperature prevailing inthe exhaust-gas aftertreatment device and by the fuel/air ratio usedduring the combustion in the combustion engine. In order, for example,to realize adequate conversion performance of the exhaust-gasaftertreatment device, a certain operating temperature, the so-calledlight-off temperature, may be attained, which may be 120° C. to 250° C.

In motor vehicles driven by Otto or diesel engines, it is, for example,conventional to control the temperature of the exhaust-gasaftertreatment device so as to ensure a fast light-off of the catalyticconverter, for example in the case of an Otto engine, by temporarilysetting a late ignition angle, as a result of which the combustion isshifted partially into the outlet tract and the exhaust-gas temperatureduring the warm-up phase is increased. In the case of diesel engines, itis inter alia conventional, for example in order to assist theregeneration of soot filters, to increase the exhaust-gas temperaturefrom time to time by intake air throttling and/or intake air pre-heatingand/or by a late start of injection and/or post injection.

Likewise, in the case of motor vehicles with a so-called automaticstart-stop facility, a control regime is known which helps to preventthe temperature of the exhaust-gas aftertreatment device from fallingbelow a certain limit value, for example the light-off temperature,during a temporary stop phase. For example, EP 0 989 299 B1 discloses acontrol device for a motor vehicle engine, which control device isconfigured so as to change the state of the motor vehicle engineautomatically between a stopped state and an operating state on thebasis of a predetermined condition. In particular, the described controldevice is capable of preventing an engagement shock of a frictionalengagement or clutch device by engine torque control at the time ofstart-up of the vehicle, even if the engine torque control is notpossible. To determine whether or not engine torque control can becarried out, it is proposed inter alia that the temperature of acatalytic converter be determined, and that a torque reduction not becarried out if said temperature is lower than a certain value.

In particular during operation of a combustion engine in the low-loadrange, for example at an engine output power of less than approximately20 Nm or when the engine is being used as an engine brake, the stabilityof the combustion is a problem which cannot be disregarded with regardto a post-injection calibration. Furthermore, at a relatively lowcombustion pressure within the respective engine cylinder, there is anincreased tendency for the fuel injected into the cylinder toprecipitate on the cylinder interior walls. This leads to excessivecontamination of the engine oil. Furthermore, the attainment of highexhaust-gas temperatures, for example for the regeneration of sootfilters, is particularly difficult in the low-load range in particularin the case of diesel engines on account of the combustion thereof,which is already lean out of principle.

The inventors have recognized the above issues and provide a solutionherein to at least partly address them. A method for controlling anexhaust-gas aftertreatment device of a vehicle hybrid drive is provided.The method comprises operating the hybrid drive only by a combustionengine, only by a non-combustion motor, or by both, as a function of atemperature of the exhaust aftertreatment device, and conducting exhaustgas of the hybrid drive at least partially through the exhaustaftertreatment device, the engine and motor each providing output topower the vehicle.

In this way, the temperature of the aftertreatment device may becontrolled by controlling the extent to which the exhaust gases producedby the engine are conducted through the device. For example, if theexhaust temperature is greater than the temperature of the device andthe device is currently operating at a temperature lower than desired,the hybrid drive may be operated by only the engine in order to quicklyheat up the device. Thus, this permits optimum operation of theexhaust-gas aftertreatment device in particular with regard toexhaust-gas purification or conversion performance.

It is pointed out that the features specified individually in the patentclaims may be combined with one another in any desired technologicallymeaningful way and discloses further embodiments of the presentdisclosure. The description, in particular in conjunction with thefigures, characterizes and specifies the disclosure further.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of a vehicle system according to anembodiment of the disclosure.

FIG. 2 shows a schematic depiction of an engine system according to anembodiment of the disclosure.

FIG. 3 shows a flow diagram depicting an exemplary embodiment of amethod according to the disclosure.

FIG. 4 shows a flow diagram depicting an exemplary embodiment of afurther method according to the disclosure.

FIG. 5 shows a flow diagram depicting an exemplary embodiment of anothermethod according to the disclosure.

DETAILED DESCRIPTION

Hybrid drive systems for motor vehicles rely on both an engine and amotor to provide torque to propel the vehicle. Under some conditions, itmay be advantageous to operate both the engine and the motorsimultaneously, while under other conditions, it may advantageous tooperate only the motor or only the engine. In embodiments describedherein, the operation of the hybrid drive may be adjusted based on anexhaust aftertreatment device coupled to the engine. An example vehiclesystem including a hybrid drive is depicted in FIGS. 1 and 2. Examplemethods for adjusting the hybrid drive based on an exhaustaftertreatment device are depicted in FIGS. 3-5.

FIG. 1 illustrates an example vehicle propulsion system 100. Vehiclepropulsion system 100 includes a fuel burning engine 10 and a motor 120.As a non-limiting example, engine 10 comprises an internal combustionengine and motor 120 comprises an electric motor. Motor 120 may beconfigured to utilize or consume a different energy source than engine10. For example, engine 10 may consume a liquid fuel (e.g. gasoline) toproduce an engine output while motor 120 may consume electrical energyto produce a motor output. As such, a vehicle with propulsion system 100may be referred to as a hybrid electric vehicle (HEV).

Vehicle propulsion system 100 includes wheels 102. Torque is supplied towheels 102 via engine 10 and transmission 104. In some embodiments,motor 120 may also provide torque to wheels 102.

Vehicle propulsion system 100 may utilize a variety of differentoperational modes depending on operating conditions encountered by thevehicle propulsion system. Some of these modes may enable engine 10 tobe maintained in an off state where combustion of fuel at the engine isdiscontinued. For example, under select operating conditions, motor 120may propel the vehicle via transmission 104 as indicated by arrow 122while engine 10 is deactivated.

During other operating conditions, motor 120 may be operated to chargean energy storage device such as battery 108. For example, motor 120 mayreceive wheel torque from transmission 104 as indicated by arrow 122where the motor may convert the kinetic energy of the vehicle toelectrical energy for storage at battery 108. Thus, motor 120 canprovide a generator function in some embodiments. However, in otherembodiments, alternator 110 may instead receive wheel torque fromtransmission 104, or energy from engine 10, where the alternator 110 mayconvert the kinetic energy of the vehicle to electrical energy forstorage at battery 108.

During still other operating conditions, engine 10 may be operated bycombusting fuel received from a fuel system (not shown in FIG. 1). Forexample, engine 10 may be operated to propel the vehicle viatransmission 104 as indicated by arrow 112 while motor 120 isdeactivated. During other operating conditions, both engine 10 and motor120 may each be operated to propel the vehicle via transmission 104 asindicated by arrows 112 and 122, respectively. A configuration whereboth the engine and the motor may selectively propel the vehicle may bereferred to as a parallel type vehicle propulsion system. Note that insome embodiments, motor 120 may propel the vehicle via a first drivesystem and engine 10 may propel the vehicle via a second drive system.

Operation in the various modes described above may be controlled by acontroller 12. Controller 12 will be described below in more detail withrespect to FIG. 2.

FIG. 2 shows a schematic depiction of additional components of vehiclepropulsion system 100. The vehicle system 100 includes an engine system8, a control system 14, and a fuel system 18. The engine system 8 mayinclude an engine 10 having a plurality of cylinders 30. The engine 10includes an engine intake 23 and an engine exhaust 25. The engine intake23 includes a throttle 62 fluidly coupled to the engine intake manifold44 via an intake passage 42. The engine exhaust 25 includes an exhaustmanifold 48 leading to an exhaust passage 35 that routes exhaust gas tothe atmosphere. The engine exhaust 25 may include one or more emissioncontrol devices 70, which may be mounted in a close-coupled position inthe exhaust. One or more emission control devices may include athree-way catalyst, selective catalytic reduction (SCR) system, lean NOxtrap, diesel particulate filter, oxidation catalyst, etc. Emissioncontrol device 70 may utilize reducants in the exhaust stream, such asurea or unburnt fuel, to reduce substrates such as NOx and CO in theexhaust. As such, emission control device 70 may include a reductantinjector. In other embodiments, reductants may be introduced via a fuelinjection system in the engine. It will be appreciated that othercomponents may be included in the engine such as a variety of valves andsensors.

Fuel system 18 may include a fuel tank 20 coupled to a fuel pump system21. The fuel pump system 21 may include one or more pumps forpressurizing fuel delivered to the injectors of engine 10, such as theexample injector 66 shown. While only a single injector 66 is shown,additional injectors are provided for each cylinder. It can beappreciated that fuel system 18 may be a return-less fuel system, areturn fuel system, or various other types of fuel system.

The fuel tank 20 may hold a plurality of fuel blends, including fuelwith a range of alcohol concentrations, such as various gasoline-ethanolblends, including E10, E85, gasoline, diesel, etc., and combinationsthereof.

The vehicle system 100 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 and temperature sensor 127 located upstream of the emissioncontrol device, and airflow sensor 125, exhaust gas sensor 128, andtemperature sensor 129 located downstream of the emission controldevice. Other sensors such as pressure, temperature, air/fuel ratio, andcomposition sensors may be coupled to various locations in the vehiclesystem 100. As another example, the actuators may include fuel injector66 and throttle 62.

The control system 14 may include a controller 12 comprising a computerreadable storage medium comprising instructions that may be executed tocarry out one more control routines. The controller may receive inputdata from the various sensors, process the input data, and trigger theactuators in response to the processed input data based on instructionor code programmed therein corresponding to one or more routines.Example control routines are described herein with regard to FIGS. 3-5.

The efficiency of an exhaust-gas aftertreatment device is verysignificantly dependent upon the operating temperature of theexhaust-gas aftertreatment device, and that during the operation of theexhaust-gas aftertreatment device, very different temperature windowsfor correct and optimum operation of the exhaust-gas aftertreatmentdevice play a decisive role, as will be explained below.

Typically, in Otto engines, use is made for example of catalyticreactors which, through the use of catalytic materials which increasethe rate of certain reactions, ensure an oxidation of HC and CO even atlow temperatures. If nitrogen oxides (NO_(x)) are additionally to bereduced, this may be achieved through the use of a three-way catalyticconverter, which however for this purpose which performs optimally atstoichiometric operation (λ≈1) of the Otto engine within narrow limits.Here, the nitrogen oxides NO_(x) are reduced by means of thenon-oxidized exhaust-gas components which are present, specifically thecarbon monoxides and the unburned hydrocarbons, wherein said exhaust-gascomponents are oxidized at the same time.

In combustion engines which are operated with an excess of air, that isto say for example Otto engines which operate in the lean-burn mode, butin particular direct-injection diesel engines or also direct-injectionOtto engines, the nitrogen oxides contained in the exhaust gas cannot bereduced out of principle, that is to say on account of the lack ofreducing agent.

For the oxidation of the unburned hydrocarbons and of carbon monoxide,provision is made in particular of an oxidation catalytic converter inthe exhaust-gas flow. To realize an adequate conversion, a certainoperating temperature is demanded. The so-called light-off temperaturemay be 120° C. to 250° C.

To reduce the nitrogen oxides, use is also made of selective catalyticconverters, so-called SCR catalytic converters, in which reducing agentis purposely introduced into the exhaust gas in order to selectivelyreduce the nitrogen oxides. As reducing agent, in addition to ammoniaand urea, use may also be made of unburned hydrocarbons. The latter isalso referred to as HC enrichment, with the unburned hydrocarbons beingintroduced directly into the exhaust tract or else being supplied bymeans of engine-internal measures, specifically by means of apost-injection of additional fuel into the combustion chamber after theactual combustion.

It is basically also possible to reduce the nitrogen oxide emissions bymeans of so-called nitrogen oxide storage catalytic converters. Here,the nitrogen oxides are initially absorbed, that is to say collected andstored, in the catalytic converter during a lean-burn mode of thecombustion engine before being reduced during a regeneration phase forexample by means of substoichiometric operation (for example λ<0.95) ofthe combustion engine with a lack of oxygen. Further possibleengine-internal measures for realizing rich, that is to saysubstoichiometric operation of the combustion engine are exhaust-gasrecirculation and, in the case of diesel engines, throttling in theintake tract. It is possible to dispense with engine-internal measuresif the reducing agent is introduced directly into the exhaust tract, forexample by means of an injection of additional fuel. During theregeneration phase, the nitrogen oxides are released and convertedsubstantially into nitrogen dioxide (N₂), carbon dioxide (CO₂) and water(H₂O). The frequency of the regeneration phases is determined by theoverall emissions of nitrogen oxides and the storage capacity of thenitrogen oxide storage catalytic converter.

The temperature of the storage catalytic converter should preferably liein a temperature window between 200° C. and 450° C., such that firstly afast reduction of the nitrogen oxides is ensured and secondly nodesorption without conversion of the re-released nitrogen oxides takesplace, such as may be triggered by excessively high temperatures.

One difficulty in the use of the storage catalytic converter in theexhaust track arises from the sulfur contained in the exhaust gas, whichsulfur is likewise absorbed in the storage catalytic converter and maybe regularly removed by means of a desulfurization. For this purpose,the storage catalytic converter may be heated to high temperatures,usually of between 600° C. and 700° C., and supplied with a reducingagent, which in turn can be attained by means of a transition to richoperation of the combustion engine. The higher the temperature of thestorage catalytic converter is, the more effective the desulfurizationis, wherein an admissible maximum temperature may not be exceeded,because then the desulfurization of the storage catalytic convertercontributes significantly to the thermal aging of the storage catalyticconverter as a result of excessively high temperatures. This adverselyaffects the desired conversion of the nitrogen oxides toward the end ofthe service life of the catalytic converter, wherein in particular thethermal storage capacity decreases as a result of thermal aging.

To minimize the emissions of soot particles, use is made of so-calledregenerative particle filters which filter the soot particles out of theexhaust gas and store them, with said soot particles being burned offintermittently during the course of the regeneration of the filter,usually at high temperatures of around 550° C. Here, the regenerationintervals are determined inter alia by the exhaust-gas back pressure,which is generated as a result of the increasing flow resistance of thefilter on account of the increasing particle mass in the filter.

Since both the exhaust gases of Otto engines and also the exhaust gasesof diesel engines contain unburned hydrocarbons (HC), carbon monoxide(CO), nitrogen oxides (NO_(x)) and also soot particles—albeit indifferent quantities and qualities—use is generally made of combinedexhaust-gas aftertreatment devices which comprise one or more of theabove-described catalytic converters and/or filters.

The increasing use of hybrid drives, in which conventionally in eachcase a combustion engine and an electric motor provide an output power,for example for driving a motor vehicle, offers completely newpossibilities for the control of exhaust-gas aftertreatment devices, inparticular with regard to optimum exhaust-gas purification or conversionperformance under different operating conditions.

For efficient control, it is advantageous for suitable measurementdevices, for example temperature sensors and/or flow sensors and/orsensors for determining chemical substances or elements contained in theexhaust-gas flow, to be provided in or near the exhaust-gas treatmentdevice, in particular upstream and/or downstream of the exhaust-gasaftertreatment device as viewed in the exhaust-gas flow direction. It isthereby possible to determine the temperature window suitable for therespective optimum operation of the exhaust-gas aftertreatment device,and if appropriate to adapt or change said temperature window to certainoperating states of the exhaust-gas aftertreatment device, for examplefor the regeneration of a soot particle filter and/or of a nitrogenoxide storage catalytic converter.

FIG. 3 illustrates a flow diagram depicting an exemplary embodiment of afirst method 300 according to the disclosure. In the exemplaryembodiment described below, the method 300 according to the disclosureis used for controlling an exhaust-gas aftertreatment device of a hybriddrive. The hybrid drive comprises a combustion engine, in particular adiesel engine, and a non-combustion motor, in particular an electricmotor. The output power provided by the combustion engine andnon-combustion motor for the hybrid drive is used, in the presentexemplary embodiment, for driving a motor vehicle. Here, the outputpower may be provided by only the combustion engine, by only thenon-combustion motor, or in a mixed operating mode, in which the totaloutput power of the hybrid drive is composed of both the output power ofthe combustion engine and also the output power of the non-combustionmotor. Furthermore, in the described exemplary embodiment, thenon-combustion motor, in particular the electric motor, can likewise beused as a generator for charging an electric storage medium, inparticular a battery, when not being used as a motor. In the describedexemplary embodiment, the exhaust gases of the hybrid drive, inparticular the exhaust gases of the combustion engine, are conductedentirely through the exhaust-gas aftertreatment device by means of acorresponding exhaust tract.

Method 300 comprises, at 302, determining whether the temperature of theexhaust-gas after-treatment device, T(D), is lower than a thresholdvalue, T1. The threshold value is for example a maximum temperature ofthe exhaust-gas aftertreatment device below which optimum pollutantremoval from the exhaust gas, that is to say optimum conversionperformance of the exhaust-gas aftertreatment device, is attained andabove which the conversion performance of the exhaust-gas aftertreatmentdevice decreases considerably or the exhaust-gas aftertreatment deviceor parts thereof may be (thermally) damaged.

Furthermore, in the exemplary embodiment described here, the thresholdvalue is a predefinable threshold value which can in particular also bevaried during operation, such that an adaptation of the desiredtemperature window for the operation of the exhaust-gas aftertreatmentdevice is easily possible as a function of the respective operatingconditions, and optimum conversion or exhaust-gas purificationperformance of the exhaust-gas after-treatment device is ensured.

If it is identified in at 302 that the temperature of the exhaust-gasaftertreatment device is lower than the threshold value (“Yes”), themethod 300 continues to 304, in which it is determined whether theexhaust-gas temperature of the combustion engine, T(E), is higher thanthe temperature of the exhaust-gas aftertreatment device.

If it is determined in 304 that the exhaust-gas temperature of theinternal combustion engine is higher than the temperature of theexhaust-gas aftertreatment device (“Yes”), the method continues to 306,in which it is determined whether a setpoint temperature of theexhaust-gas after-treatment device is higher than the temperature of theexhaust-gas aftertreatment device.

In the described embodiment, the setpoint temperature is generally thetemperature at which the exhaust-gas aftertreatment device attains anoptimum conversion efficiency, that is to say optimum exhaust-gaspurification performance. Depending on the respective operating state ofthe exhaust-gas aftertreatment device, however, the setpoint temperaturemay likewise be a temperature at which for example effectiveregeneration of an nitrogen oxide storage catalytic converters, ammoniastorage catalytic converters and/or soot particle filters, which are/iscomprised by the exhaust-gas aftertreatment device, is attained. Saidso-called thermal desorption is permitted by temporarily raising orlowering the operating temperature of the exhaust-gas aftertreatmentdevice by means of the predefinable setpoint temperature.

If it is determined at 306 that the setpoint temperature of theexhaust-gas aftertreatment device is higher than the temperature of theexhaust-gas aftertreatment device (“Yes”), the method continues to 308,in which the hybrid drive is operated only by the combustion engine.That is to say the entire output power of the hybrid drive or the drivepower of the motor vehicle is provided by the combustion engine alone.The exhaust-gas temperature of the internal combustion engine isincreased by increasing the power output by the internal combustionengine. The non-combustion motor is either shut down or is likewisedriven by the combustion engine as a generator for charging a battery.According to the embodiment, the temperature of the exhaust-gasaftertreatment device is increased by the exhaust gas of the combustionengine.

It is pointed out that the exhaust-gas temperature of the combustionengine is, in a known way, directly related to the power demanded of oroutput by the combustion engine, the rotational speed and the combustionmethod (Otto or diesel engine). The above wording that the “exhaust-gastemperature of the combustion engine is higher than the temperature ofthe exhaust-gas aftertreatment device” accordingly includes that theexhaust-gas temperature of the combustion engine is higher, inparticular as a result of a certain load demand predefined for exampleby a user, than the temperature of the exhaust-gas aftertreatmentdevice. In other words, a high exhaust-gas temperature is to be equatedwith a high load demand or output power, and a low exhaust-gastemperature is to be equated with a low load demand or output power, andvice versa. Any wording hereinafter relating to the exhaust-gastemperature of the combustion engine or the load demand or the outputpower of the combustion engine should likewise be interpreted in thissense.

If it is identified at 306 that the setpoint temperature of theexhaust-gas aftertreatment device is not higher than the temperature ofthe exhaust-gas aftertreatment device (“No”), the method continues to310, in which the hybrid drive is operated in a mixed operating mode. Inthe mixed operating mode, the combustion engine and the non-combustionmotor simultaneously provide the output power of the hybrid drive, inparticular the drive power of the motor vehicle. In said operating mode,the non-combustion motor, in particular the electric motor, drives forexample the combustion engine, in particular the diesel engine, in orderto reduce the load demand and consequently the exhaust-gas temperatureof the combustion engine. Accordingly, a desired reduction in thetemperature of the exhaust-gas treatment device is attained by theexhaust gases of the combustion engine flowing through the exhaust-gasafter-treatment device.

In particular, the non-combustion motor preferably drives the combustionengine or assists the latter, in order to reduce the load demanded ofthe combustion engine or the power output by the combustion engine.Here, the degree of assistance by the non-combustion motor may be variedas a function of the power demanded for example by a user, in such a waythat, in the case of a low load demand, the output power of the hybriddrive is provided substantially by the combustion engine, whereas withincreasing power demand, the non-combustion motor contributes anincreasing proportion of the output power of the hybrid drive.Therefore, operation of the combustion engine substantially in alow-load range with low exhaust-gas temperatures of the combustionengine is ensured even over a wide range of load demand.

The reduced load demand on the combustion engine by the non-combustionmotor leads to a reduction in the exhaust-gas temperature of thecombustion engine, as a result of which a reduction in the temperatureof the exhaust-gas aftertreatment device can be realized as desired.

If it is identified in 304 that the exhaust-gas temperature of theinternal combustion engine is not higher than the temperature of theexhaust-gas aftertreatment device (“No”), the method continues to 312,in which it is determined whether a setpoint temperature of theexhaust-gas aftertreatment device is higher than the temperature of theexhaust-gas aftertreatment device.

If it is identified 312 that the setpoint temperature of the exhaust-gasaftertreatment device is higher than the temperature of the exhaust-gasaftertreatment device (“Yes”), the method continues to 314, in which thehybrid drive is operated only by the non-combustion motor. Duringoperation by only the non-combustion motor, the entire output power ofthe hybrid drive for driving the motor vehicle is provided by thenon-combustion motor alone, in particular the electric motor. Thecombustion engine, in particular the diesel engine, is shut down suchthat no further (cool) exhaust gases can flow via the exhaust tract tothe exhaust-gas aftertreatment device. The present temperature level ofthe exhaust-gas aftertreatment device is thereby maintained or - atleast for a certain period of time - even increased by continuingoxidation processes in the exhaust-gas aftertreatment device and thethermal energy thereby released.

If it is identified at 312 that the setpoint temperature of theexhaust-gas aftertreatment device is not higher than the temperature ofthe exhaust-gas aftertreatment device (“No”), the method continues to316, in which the hybrid drive is operated only by the combustionengine. In contrast to 308, in which the hybrid drive is likewiseoperated by only the combustion engine, the exhaust-gas temperature ofthe combustion engine is however lower, for example on account of alower load demand, than the temperature of the exhaust-gasaftertreatment device, and the exhaust gas of the internal combustionengine can therefore be used directly as desired to reduce thetemperature of the exhaust-gas aftertreatment device. The non-combustionmotor can be used in the way already described in 308.

It is however also alternatively possible at 316 for the non-combustionmotor to continue to be used in order to assist the combustion engine,as a result of which the load demand on the combustion engine is furtherreduced and the exhaust-gas temperature of the combustion engine isreduced yet further. This permits an even faster reduction of thetemperature of the exhaust-gas aftertreatment device.

If it is identified in at 302 that the temperature of the exhaust-gasaftertreatment device is not lower than the threshold value (“No”), themethod continues to 318, in which it is determined whether the oxygenconcentration in the exhaust gas should be reduced.

If it is identified at 318 that the oxygen concentration in the exhaustgas should not be reduced (“No”), the method continues to 320, in whichit is determined whether the exhaust-gas temperature of the combustionengine is lower than the temperature of the exhaust-gas aftertreatmentdevice.

If it is identified at 320 that the exhaust-gas temperature of thecombustion engine is lower than the temperature of the exhaust-gasaftertreatment device (“Yes”), the method continues to 322, in which thehybrid drive is operated only by the combustion engine. 322substantially corresponds to 314 as already described. Since theexhaust-gas temperature of the combustion engine is lower than thetemperature of the exhaust-gas aftertreatment device, the exhaust gas ofthe combustion engine can, as desired, be used directly to reduce thetemperature of the exhaust-gas aftertreatment device.

If it is determined at 320 that the exhaust-gas temperature of thecombustion engine is not lower than the temperature of the exhaust-gasaftertreatment device (“No”), the method continues to 324, in which thehybrid drive is operated in a mixed operating mode.

If it is determined at 318 that the oxygen concentration in the exhaustgas should be reduced (“Yes”), the method continues to 326, in which thehybrid drive is operated only by the non-combustion motor. Duringoperation by only the non-combustion motor, the entire output power ofthe hybrid drive for driving the motor vehicle is provided by thenon-combustion motor alone, in particular the electric motor. Thecombustion engine, in particular the diesel engine, is shut down suchthat no further exhaust gases can flow via the exhaust tract to theexhaust-gas aftertreatment device. In this way, in particular in thecase of a lean combustion, that is to say in the case of a combustionwith an excess of air, such as takes place for example in Otto enginesoperating in the lean-burn mode or in direct-injection diesel engines,the oxygen concentration in the exhaust gas is reduced. As a result ofthe reduced oxygen concentration in the exhaust gas, the conversion oroxidation processes in the exhaust-gas aftertreatment device slowabruptly. With increasing time duration, said processes come to asubstantially complete stop, as a result of which no more thermal energyfrom the oxidation processes is released. Consequently, the temperatureof the exhaust-gas aftertreatment device is reduced as desired.

322, 324, and 326 constitute alternative ways of reducing thetemperature of the exhaust-gas aftertreatment device if the temperatureof the exhaust-gas aftertreatment device has exceeded the thresholdvalue. 322 and 324 describe the possibility of thermal cooling of theexhaust-gas aftertreatment device by exhaust gas of the combustionengine, the temperature of which has been suitably reduced, whereas at326, the reduction in temperature of the exhaust-gas aftertreatmentdevice is attained by suppressing the chemical processes in theexhaust-gas aftertreatment device by reduction of the oxygenconcentration in the exhaust-gas flow. The two possibilities may beprovided in each case individually or, as in the exemplary embodimentdescribed, may be provided in parallel. In the latter case, the mostexpedient approach for the respective operating state of the hybriddrive or of the exhaust-gas aftertreatment device can be selected.

After 308, 310, 314, 316, 322, 324, or 326 explained above have beencarried out as described, the method according to the disclosure ends.It is self-evident that, during the operation of the hybrid drive or ofthe exhaust-gas aftertreatment device, the method 300 according to thedisclosure is run through anew between the start point and the end pointat predetermined regular time intervals.

In some embodiments, the respective operating mode of the hybrid drivemay be selected as a function of a predefinable spatial velocity of theexhaust-gas aftertreatment device. In a known way, the spatial velocity,by quotient formation, relates a volume flow, in this case in particularof the exhaust gas, to a spatial volume, for example of a catalyticconverter and/or filter of the exhaust-gas aftertreatment device or elseof the entire exhaust-gas aftertreatment device, wherein the reciprocalof the spatial velocity indicates the residence time.

According to this embodiment, it is therefore possible to adjust theflow speed of the exhaust gas flowing through the exhaust-gasaftertreatment device, and consequently the spatial velocity and theresidence time of the exhaust-gas flow in the exhaust-gas aftertreatmentdevice. Since the conversion efficiency of the exhaust-gasaftertreatment device is directly related to the spatial velocity orresidence time of the exhaust gas in the exhaust-gas aftertreatmentdevice, and the conversion performance is higher the lower the spatialvelocity or the longer the residence time is, it is possible to ensureoptimum operation with regard to exhaust-gas purification or conversionperformance of the exhaust-gas aftertreatment device.

The spatial velocity can be predefined, in particular also varied duringthe operation of the exhaust-gas aftertreatment device. This permits asimple adaptation to different operating conditions which demanddifferent spatial velocities for optimum operation of the exhaust-gasaftertreatment device.

FIG. 4 illustrates a flow diagram depicting an exemplary embodiment ofanother method 400 according to the present disclosure. In the exemplaryembodiment described below, said method 400 is used for controlling theexhaust-gas aftertreatment device of the hybrid drive which has alreadybeen discussed in conjunction with the description of the exemplaryembodiment shown in FIG. 3. Accordingly, the hybrid drive of the method400 explained below is of the same design, such that said design willnot be described again. However, in the method 400 described here, therespective operating mode of the hybrid drive is selected as a functionof a predefinable spatial velocity of the exhaust gases of the hybriddrive.

Proceeding from the start point of the method 400, it is determined at402 whether a low load demand for the hybrid drive or the combustionengine is present. If it is detected at 402 that a low load demand ispresent (“Yes”), the method continues to 404, in which the hybrid driveis operated only by the combustion engine, that is to say the entireoutput power of the hybrid drive or the drive power of the motor vehicleis provided by the combustion engine alone. The non-combustion motor,for example the electric motor, can be shut down in this case. Saidnon-combustion motor may then optionally be used, by the drive of thecombustion engine, as a generator for charging an electric storagemedium, in particular a battery.

Since the combustion engine is operated in a low-load range, thecombustion engine discharges the exhaust gas at a relatively low flowspeed. The low flow speed leads to a longer residence time of theexhaust gas in the exhaust-gas aftertreatment device and consequently toimproved catalytic conversion and/or filtering. The conversionefficiency of the exhaust-gas aftertreatment device is thereby improved.

It is however also alternatively possible at 404 for the non-combustionmotor to continue to be used in order to assist the combustion engine,as a result of which the load demand on the combustion engine is furtherreduced and the exhaust-gas flow speed of the combustion engine can bereduced further. In this way, it is possible to realize an even lowerspatial velocity or longer residence time, and therefore the bestpossible conversion or exhaust-gas purification performance of theexhaust-gas aftertreatment device.

If it is determined at 402 that a low load demand is not present (“No”),the method continues to 406, in which the hybrid drive is operated in amixed operating mode. In the mixed operating mode, the combustion engineand the non-combustion motor simultaneously provide the output power ofthe hybrid drive, in particular the drive power of the motor vehicle. Insaid operating mode, the non-combustion motor, in particular theelectric motor, drives for example the combustion engine, in particularthe diesel engine, in order to reduce the load demand and consequentlythe exhaust-gas flow speed of the combustion engine.

The degree of assistance by the non-combustion motor may preferably beadapted as a function of the power demanded for example by the user, insuch a way that, in the case of a relatively low load demand, the outputpower of the hybrid drive is provided substantially by the combustionengine, whereas with increasing power demand, the non-combustion motorcontributes a greater proportion of the output power of the hybriddrive. Therefore, operation of the combustion engine substantially in alow-load range with a low flow speed of the exhaust gas is ensured evenover a wide range of load demand.

The reduced power demand on the combustion engine by the non-combustionmotor thus leads, despite the higher load demand on the hybrid drive, toa longer residence time of the exhaust gas in the exhaust-gasaftertreatment device, as a result of which the purification orconversion performance of the exhaust-gas aftertreatment device isimproved.

After 404 or 406 explained above have been carried out as described, themethod ends. It is self-evident that, during the operation of the hybriddrive or of the exhaust-gas aftertreatment device, the method 400 is runthrough anew between the start point and the end point at predeterminedregular time intervals.

Furthermore, according to another embodiment of the present disclosure,the spatial velocity can be predefined, in particular also varied duringthe operation of the exhaust-gas aftertreatment device. This permits asimple adaptation of the method according to the disclosure to differentoperating conditions which utilize different spatial velocities foroptimum operation of the exhaust-gas aftertreatment device.

FIG. 5 illustrates a flow diagram depicting an exemplary embodiment of amethod 500 according to the present disclosure. In the exemplaryembodiment described below, said method 500 is used for controlling theexhaust-gas aftertreatment device of the hybrid drive which has alreadybeen discussed in conjunction with the description of the exemplaryembodiment shown in FIGS. 3 and 4. Accordingly, the hybrid drive of themethod 500 explained below is of the same design, such that said designwill not be described again. In the method 500 described here, therespective operating mode of the hybrid drive is selected as a functionof both temperature and a predefinable spatial velocity of the exhaustgases of the hybrid drive.

Method 500 comprises, at 502, determining if the temperature of theaftertreatment device is equal to a desired temperature. The desiredtemperature of the device may be any suitable temperature for thecurrent operating conditions. For example, if the device is in normaloperation, the desired temperature may be the light-off temperature. Inother conditions, such as when it is indicated the device is to beregenerated, the desired temperature may be higher than light-offtemperature. If it is determined that the temperature of the device isat the desired temperature, method 500 proceeds to 504 to determine ifthe spatial velocity (SV) of the exhaust flowing through the device isat a desired spatial velocity. As explained above, the lower the spatialvelocity of the exhaust, the greater the conversion performance of theaftertreatment device due to the longer residence time of the exhaust inthe device. In order to increase the conversion performance, the spatialvelocity may be adjusted by adjusting the amount of exhaust flowingthrough the device. In order to determine the desired spatial velocity,one or more of the age of the device, the type of device, the size ofthe device, exhaust temperature, and the current operating state of thedevice may be considered. For example, older aftertreatment devices mayhave reduced conversion efficiencies and thus may have lower optimalspatial velocities. If it is determined that the current spatialvelocity is equal to the desired spatial velocity for the currentconditions, method 500 proceeds to 506 maintain current operatingparameters in order to continue to deliver exhaust at the currenttemperature and flow rate.

If it is determined at 504 that the current spatial velocity is notequal to the desired spatial velocity, method 500 proceeds to 508 todetermine if the current spatial velocity is greater than the desiredvelocity. If it is determined that the current velocity is greater thanthe optimal velocity, the amount of load placed on the motor may beincreased at 510 to reduce the load on the engine and thus reduce thespatial velocity by reducing the exhaust flow. In some embodiments,depending on current overall driver-requested torque and the amount ofthe desired spatial velocity, the load placed on the motor may beincreased such that all wheel torque is provided by the motor. In otherembodiments, the engine may continue to provide a portion of the torque.

If it is determined that the current spatial velocity is less than thedesired velocity, method 500 proceeds to 512 to decrease the load placedon the motor and increase the load placed on the engine to increase flowthrough the aftertreatment device. In some embodiments, the motor maystill provide a portion of the torque to the wheels, while in otherembodiments, the engine may provide all the requested torque. Further,in some embodiments, additional action may be taken to increase exhaustflow, such as opening the throttle, adjusting spark timing, etc. After506, 510, and 512, method 500 proceeds to return to the beginning of themethod to continually ensure the temperature of the exhaust device is atan optimum, desired temperature, and that the spatial velocity is at adesired velocity for current operating conditions.

Returning to 502, if it is determined that the aftertreatment device isnot operating at a desired temperature, method 500 proceeds to 514 todetermined if the temperature of the device is above the desiredtemperature. If the temperature of the device is above the desiredtemperature, method 500 proceeds to 516 to determine if the temperatureof the exhaust is less than the temperature of the device. If theexhaust temperature is less than the device temperature, the exhaust maybe used to cool the device down to the desired temperature. Thus, at518, the hybrid drive is operated by only the engine. If the exhausttemperature is greater than the device temperature, the motor may beoperated to provide some of the driver-requested torque, and the enginemay provide torque as well.

If, at 514, it is determined that the temperature of the device is notgreater than the desired temperature, method 500 proceeds to 522 todetermine if the exhaust temperature is greater than the devicetemperature. If so, the exhaust may be used to heat the device, and thusat 524, the hybrid drive is operated by only the engine. If the exhausttemperature is not greater than the device temperature, both the motorand engine may be operated at 526 so that the exhaust does not continueto cool the device at an undesirable rate.

After 518, 520, 524, and 526, method 500 proceeds to return to determineif the device temperature is at the desired temperature. This way, afteradjusting the relative loads on the engine and motor based on devicetemperature, if it is determined that the device has been brought to thedesired temperature, the hybrid drive may be operated as a function ofthe spatial velocity, as described above.

Thus, the methods described with respect to FIGS. 4 and 5 provide foroperating the hybrid drive as a function of a desired spatial velocityof the exhaust aftertreatment device. In one embodiment, a method forcontrolling the exhaust aftertreatment device of the hybrid drivecomprises operating a combustion engine and a non-combustion motor whicheach provide an output drive power, including operating only thecombustion engine, only the non-combustion motor, or by both thecombustion engine and the non-combustion motor, as a function of anexhaust spatial velocity of the aftertreatment device. The desiredspatial velocity of exhaust flowing through the aftertreatment devicemay be based on an age of the device, a type of the device, a size ofthe device, exhaust temperature, and a current operating state of thedevice. In another embodiment, a controller may control the hybrid driveto adjust a load placed on the motor based on the desired spatialvelocity of exhaust flowing though the aftertreatment device.

The methods according to the present disclosure for controlling anexhaust-gas aftertreatment device of a hybrid drive is self-evidentlynot restricted to the exemplary embodiments described herein and shownin the figures. With regard to the present disclosure, it is for examplenot of importance whether the combustion engine and the non-combustionmotor provide their respective output powers in series or in parallel.Corresponding serial and/or parallel engine drive arrangements, inparticular such as serve for the propulsion of a motor vehicle, are wellknown to a person skilled in the art and are therefore also encompassedby the present disclosure.

Furthermore, for the embodiments described herein, it does not matterwhether the combustion engine is an Otto engine or a diesel engine orany other type of engine whose working principle is based on thecombustion of a fuel and which therefore produces an exhaust gas to betreated, for example purified of pollutants, by an exhaust-gasaftertreatment device. In contrast, the non-combustion motor may be forexample an electric motor. Within the context of the present disclosure,however, said non-combustion motor may also be any other type ofnon-combustion motor which produces substantially no exhaust gas to beaftertreated or purified. Here, “exhaust gas not to be aftertreated”also means an exhaust gas which has considerably lower pollutantconcentrations than the exhaust gas of the combustion engine or even hasno pollutant concentrations, and which therefore requires substantiallyno aftertreatment. Accordingly, an electric motor operated by means of afuel cell is also to be regarded as a non-combustion motor within thecontext of the present disclosure.

In a preferred embodiment, the methods according to the disclosure areused for controlling an exhaust-gas aftertreatment device of a hybriddrive for a motor vehicle, the hybrid drive comprising at least onecombustion engine, in particular a diesel engine, and at least onenon-combustion motor, in particular an electric motor, by the drivepower of the hybrid drive for the propulsion of the motor vehicle isprovided either by only the combustion engine or by only thenon-combustion motor or in a mixed operating mode in which both thecombustion engine and also the non-combustion motor output theirrespective output power simultaneously, and the operating mode of thehybrid drive is selected as a function of a predefinable temperature ofthe exhaust-gas aftertreatment device and/or a predefinable spatialvelocity of the exhaust gases of the hybrid drive.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,1-4, 1-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for controlling an exhaustaftertreatment device of a vehicle hybrid drive, comprising: operatingthe hybrid drive to drive a vehicle via power produced in one modeselected from a group of three modes including a mode of driving thevehicle only by a combustion engine, a mode of driving the vehicle onlyby a non-combustion motor, or a mode of driving the vehicle by thecombustion engine and the non-combustion motor, the one mode being afunction of a temperature of the exhaust aftertreatment device, whereinthe hybrid drive is operated to drive the vehicle via power producedonly by the combustion engine if the temperature of the exhaustaftertreatment device is higher than a threshold value and an exhausttemperature of the combustion engine is lower than the temperature ofthe exhaustafter treatment device, and wherein the hybrid drive isoperated to drive the vehicle via power produced in a mixed operatingmode if the temperature of the exhaust aftertreatment device is higherthan the threshold value and the exhaust gas temperature of thecombustion engine is higher than the temperature of the exhaustaftertreatment device; and conducting exhaust gas of the hybrid drive atleast partially through the exhaust aftertreatment device, the engineand motor each capable of providing output to power the vehicle.
 2. Themethod as claimed in claim 1, further comprising setting a setpointtemperature of the exhaust aftertreatment device based on a desiredstate of the exhaust aftertreatment device.
 3. The method as claimed inclaim 2, wherein the hybrid drive is operated to drive the vehicle viapower produced only by the combustion engine when: the temperature ofthe exhaust aftertreatment device is lower than the threshold value; theexhaust gas temperature of the combustion engine is higher than thetemperature of the exhaust aftertreatment device; and the setpointtemperature of the exhaust aftertreatment device is higher than thetemperature of the exhaust aftertreatment device.
 4. The method asclaimed in claim 2, wherein the hybrid drive is operated to drive thevehicle via power produced only by the non-combustion motor when: thetemperature of the exhaust aftertreatment device is lower than thethreshold value; the exhaust gas temperature of the combustion engine islower than the temperature of the exhaust aftertreatment device; and thesetpoint temperature of the exhaust aftertreatment device is higher thanthe temperature of the exhaust aftertreatment device.
 5. The method asclaimed in claim 2, wherein the hybrid drive is operated to drive thevehicle via power produced by both the engine and the motor when: thetemperature of the exhaust aftertreatment device is lower than thethreshold value; the exhaust gas temperature of the combustion engine ishigher than the temperature of the exhaust aftertreatment device; andthe setpoint temperature of the exhaust aftertreatment device is lowerthan the temperature of the exhaust aftertreatment device.
 6. The methodas claimed in claim 2, wherein the hybrid drive is operated to drive thevehicle via power produced only by the combustion engine when: thetemperature of the exhaust aftertreatment device is lower than thethreshold value; the exhaust gas temperature of the combustion engine islower than the temperature of the exhaust aftertreatment device; and thesetpoint temperature of the exhaust aftertreatment device is lower thanthe temperature of the exhaust aftertreatment device.
 7. The method asclaimed in claim 1, wherein operating the hybrid drive to drive thevehicle via power produced by only the combustion engine furthercomprises operating the non-combustion motor and routing power producedby the motor to an energy storage device.